This invention is related to a tandem brake power booster for automotive vehicles of the type having a housing whose internal space is subdivided into a front and a rear booster chamber by means of a partition wall, a first and a second movable wall which subdivide the front and the rear booster chamber into a first vacuum chamber and a first power chamber and a second vacuum chamber and a second power chamber, respectively. A control housing is slidable in the direction of actuation and a valve device which is accommodated therein, is actuatable by means of an operating rod linked to a brake pedal and controls the passage of atmospheric air into the power chambers. A push rod interacts with the control housing and transmits the brake power to an actuating piston of a master cylinder secured to the housing. The vacuum chambers as well as the power chambers are connected to each other in a range which is located within their radially internal boundary.
A tandem brake power booster of this kind is known, for example, from the German patent application No. P 33 03 577, published without examination. The special feature of this brake power booster is that the link between the two power chambers is established by means of an annular clearance which is defined between a guide tube pushed onto the control housing and a metal sleeve fastened to the control housing concentrically with respect to the guide tube, whereas the vacuum chambers are connected to each other through vacuum ducts being formed out in the control housing and radially defined by the inner wall of the sleeve. In this configuration, the guide tube extends into the front power chamber and projects through a partition wall which subdivides the booster housing into two booster chambers and is sealed off against the guide tube by means of a sealing ring. The annular clearance is subdivided into individual ventilating ducts by a plurality of radial fins formed at the internal diameter and the anterior movable wall is in active connection with the control housing through the sleeve.
One shortcoming of the forementioned tandem brake power booster is the necessity to utilize a plurality of components for the simultaneous ventilation of the power chambers which causes considerable problems with regard to their sealing, particularly in the range of the partition wall on the surface of the guide tube and of the two O-rings which seal off the sleeve against the control housing.